OAKLAND, Calif. -- When a patent expires on a brand-name prescription drug, manufacturers rush to make a generic. Patients and insurance companies like them because they're almost always less expensive. However, some critics are asking if generic options are equally safe.

63-year-old cancer patient Maggie Dowling of Pittsburg found out the hard way. A generic version of her pain medicine made her sick.

"Every drug has its potential for harmful side effects. It's just that I want to have as few side effects as possible, I have had some serious reactions," explains Dowling.

She's not alone. After switching to generic drugs, thousands of patients have complained to federal regulators and others.

Compared to brand name medicines, the generic versions look different. That's on purpose. The FDA requires their effect be equivalent, but there can still be trouble.

Consider the case of a well-known, brand-name antidepressant, Wellbutrin 300 milligram xl and its generic. They look different and tests show they act very differently in the body.

Wellbutrin-XL releases gradually over time, peaking at about eight hours before tapering off. But the generic equivalent delivers a much stronger initial dose. Despite complaints from hundreds of patients about irritability, nausea and worsened depression, the FDA has taken no action.

UC San Francisco Professor and Ross Valley pharmacist Paul Lofholm says the trouble is in the generic drug's less-strictly regulated fillers and pill size.

"It would still contain the right amount of drug, but it would behave differently," says Prof. Lofholm.

In fact, generic blood pressure medicines and seizure medicines have had similar problems. Lofholm advises when switching to generics or changing manufacturers, patients should pay very close attention to how they feel.

"They're the people that take the drug, They're the ones that get the response," says the professor.

Insurers often pressure consumers to switch to generic drugs because they're cheaper. Most generics are trouble free, but there remains what some call a looming drug disaster.

Imports account more than 80 percent of American generic drugs and raw materials.

Former FDA official turned advocate William Hubbard works with the Alliance for a Stronger FDA. He points to 81 U.S. deaths this year from a generic blood thinner Heparin. Investigators say a Chinese supplier deliberately used a cheap chemical substitute to boost profits.

"The FDA is increasingly concerned about the quality of generics because of the widespread sourcing in less developed countries," says Hubbard.

And U.S. investigators are suing a major generic drug maker in India over what they say is the use of unapproved ingredients and lying to the FDA in a quote "pattern of fraud."

"Someone can substitute a dangerous ingredient in a drug and Americans can be injured. And I think that will continue to happen until we find a way to strengthen the FDA," states Hubbard.

Consumer watchdog Jerry Flanagan says the FDA and state regulators are outmatched: "The problem is that the FDA that's supposed to be overseeing generic and brand-name drugs is asleep at the switch."

Even federal officials admit they need to spend at least $200 million a year more on overseas inspections.

Maggie Dowling says she's now extra careful, but worries about people who may just trust what's in the bottle.

"And the bottom line is that the people are dying," says Dowling

This week the FDA announced that some permanent drug inspectors are to be stationed in China, India and other countries beginning next year.

Critics say that's a start, but that the agency is still overwhelmed and understaffed and, more importantly, Americans under-protected.